Role of plant hormones and small signalling molecules in nodulation under P stress

Plant hormones and other mobile signalling elements play key roles in regulating nodulation and N₂ fixation in legumes. This includes many hormones associated with regulating general growth and development, such as cytokinin, auxin, gibberellins and strigolactones and plant hormones associated with response to stress, including ethylene. Mobile peptides and microRNAs have also shown to have significant roles in regulating nodule initiation, organogenesis and nutrient response. In this chapter we will discuss the roles of these small signalling molecules in nodulation, highlighting specific examples of their interactions with phosphorous (P) stress. P-induced small peptides and microRNAs have been identified in legumes, but the role of these signals in regulating nodulation response to P stress has not been directly investigated. Similarly, relatively few studies that have specifically examined the role of plant hormones in P response of nodulation and areas for future research are highlighted.